There has been an increasing interest in the ability to measure position of the fingers and hand in such areas as virtual reality, telerobotics, graphical animation and medical hand function assessment. There have been a number of hand-measurement devices constructed to date for measuring the position of the fingers; however, each such finger-measuring device has a common inadequacy, among various other shortcomings. The primary inadequacy of the devices being that they measure joint angles of the hand and then rely upon a mathematical model of the physical hand and xe2x80x9cforward kinematicxe2x80x9d mathematical calculations to produce an estimate of fingertip positions. Measuring finger joint angles explicitly is satisfactory when the goal of the device is to be used for measuring joint angles. However, in many of the aforementioned fields of study, the desired parameter to be measured is the position of the fingertip. When the position of the fingertip is desired, by measuring the finger joint angles and combining these angles with the mathematical model of the hand, errors in both the joint angle measurements and the model add to produce a cumulative error in fingertip position.
One common source of error is introduced by employing a simplified mathematical model of the hand, where each joint is approximated as a revolute joint with a fixed axis of rotation. More realistically, the instantaneous joint axis of a finger actually varies as a function of the joint angle. Additionally, measuring the joint angles of the finger often requires that a goniometer be affixed to phalanges comprising the links by the joint. Any unmeasured relative motion between these affixation points and the phalanges introduces error in the joint measurement. Hence, the number of such unmeasured affixation points is preferably kept to a minimum.
Devices which illustrate the above deficiencies are exemplified by the gloves described in U.S. Pat. Nos. 4,542,291, 4,937,444, 5,047,952, 5,280,265, 4,986,280, 5,086,785, 4,414,537, 5,184,009, 4,444,205, 5,316,017, 4,715,235.
Methods and devices are provided for accurately determining the positions of animate links and angles of animate joints of an animate kinematic chain of an animate body. The animate body comprises a plurality of animate links interconnected by animate joints to provide the animate kinematic chain. The device comprises a plurality of rigid device links interconnected by fixed-axis revolute device joints to provide a device kinematic chain. Two of the device kinematic chain links are terminal device links, each held in known rigid relationship to an animate link, designated as the terminal animate links, via attachment means. At least one of the device joints is displaced away from the animate links. There are at least three device joints with two sensing device joints on opposing ends of a device link. The sensing device joints provide for measurement of device joint angles. The number of sensing device joints is at least sufficient to determine the relative placement of the two terminal device links. The angle of each of said sensing device joints is measured and transmitted as a signal to a signal processor. The signal processor determines the relative placement of the terminal device links using said signals and using forward kinematic mathematical techniques on the device kinematic chain. Further, employing knowledge of the placement of the terminal device links relative to the terminal animate links, the signal processor can calculate the relative placement of the terminal animate links. By using the relative placement of the terminal animate links, and a kinematic model of the animate body, which includes modeled animate links and animate joints, the positions of such animate links and the angles of such animate joints can be calculated using inverse kinematic mathematical techniques. The subject invention finds particular application with the hand.